This invention relates broadly to lenses and polymeric materials useful in optic and ophthalmic arts. More specifically, this invention relates to polymeric materials, contact lenses and treatment processes useful in the manufacture of contact lenses.
A wide variety of research has been conducted in the field of biocompatible polymers. The definition of the term xe2x80x9cbiocompatiblexe2x80x9d depends on the particular application for which the polymer is designed. In the field of ophthalmic lenses, and in particular in the field of contact lenses, a biocompatible lens is generally defined as one that does not substantially damage the surrounding ocular tissue and ocular fluid during the time period of contact. The phrase xe2x80x9cophthalmically compatiblexe2x80x9d more appropriately describes the biocompatibility requirements of ophthalmic lenses.
One ophthalmic compatibility feature for contact lenses is that the lens permits oxygen to reach the cornea in an amount that is sufficient for long-term corneal health. The contact lens should permit oxygen from the surrounding air to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissues. If sufficient oxygen does not reach the cornea, corneal swelling can occur, as can epithelial microcysts, stromal/epithelial thinning, stromal acidosis, endothelial polymegethism, corneal ulcers and increased inflammation. Brennan et al., Opt. Vis. Sci., 74(8):609-623 (1997). xe2x80x9cSoftxe2x80x9d contact lenses conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Thus, soft contact lenses should permit oxygen to diffuse through the lens to reach the cornea.
Another ophthalmic compatibility feature for soft contact lenses is that the lens not adhere strongly to the eye. Clearly, the consumer should be able to easily remove the lens from the eye for disinfecting, cleaning or disposal. Moreover, the lens should also be able to move on the eye in order to encourage tear flow between the lens and the eye. Tear flow between the lens and eye permits debris, such as foreign particulates or dead epithelial cells, to be swept from beneath the lens and, ultimately, out of the eye in tear fluid. Thus, a contact lens should not adhere to the eye so strongly that adequate movement of the lens on the eye is inhibited.
Although there exist rigid gas permeable (xe2x80x9cRGPxe2x80x9d) contact lenses that have high oxygen permeability and that move on the eye, RGP lenses are typically quite uncomfortable for the consumer. Many consumers therefore prefer soft contact lenses. Moreover, a contact lens that can be continuously worn for a period of a day or more (including wear during periods of sleeping) implies comfort levels that exclude RGP lenses as popular extended-wear candidates.
In order to balance the ophthalmic compatibility and consumer comfort requirements in designing a daily wear soft contact lens, polymers and copolymers of 2-hydroxyethyl methacrylate (HEMA), N-vinyl pyrrolidone and glyceryl methacrylate (GMA) were developed. These hydrophilic polymers move well on the eye and provide sufficient oxygen permeability for daily wear (e.g. about 8-35 Dk units). The FDA has approved certain soft contact lenses for extended wear periods of up to about six nights of overnight wear and seven days of daily wear. However, the consumer cannot safely and comfortably wear these poly(HEMA) lenses for extended periods of seven days or more, because the oxygen permeability is insufficient. True extended wear (i.e., seven days or more) of these lenses can result, at a minimum, in corneal swelling and development of surface blood vessels in the cornea. In order to improve oxygen permeability, polymers containing silicone groups were developed. Many siloxane-containing polymers have been disclosed as having high oxygen permeability. [For example, see U.S. Pat. Nos. 3,228,741; 3,341,490; 3,996,187; and 3,996,189.] However, contact lenses made using those known polysiloxanes often adhere to the eye, inhibiting the necessary lens movement. Polysiloxanes are typically highly lipophilic, which causes a haze of lipids and proteins to form that interferes with vision through the lens.
There have been attempts to blend the desirable properties of hydrophilic polymers, formed from monomers such as HEMA, with the desirable oxygen permeability of polymers formed from siloxane-containing monomers. [For example, see U.S. Pat. Nos. 3,808,178; 4,136,250; 4,711,943; 5,070,169 and 5,760,100.] However, prior attempts at producing a true extended-wear contact lens have not been particularly successful, either because of the effect of the extended-wear lens on corneal health or because the lens would not move on the eye. Thus, oxygen permeabilities remained too low and/or the lenses adhered to the corneas.
Thus, there remains a need for an ophthalmically compatible, transparent polymeric material that is suited to prolonged periods of continuous contact with ocular tissue and tear fluid. The discussion that follows discloses such materials, contact lenses made from those materials and processes for preparing the lenses.
It has been discovered that the co-polymerization of a (a) hydrophilic monomer with (b) a wide variety of hydrophobic monomers (both aliphatic and aromatic), (c) a tris(siloxy)silyl group-containing monomer, and usually a (d) polyfluorinated monomer and optional monomers or monomer mixtures that can include a cationic monomer, a non-aromatic hydrophobic monomer and a poly(dimethylsiloxy)silyl group-containing monomer, provides a polymer that has substantially greater water content, while maintaining exceptional oxygen permeability.
Thus, the present invention contemplates an ophthalmic lens comprising a polymeric material that has an oxygen permeability of about 45 to about 150 Dk units and a hydrated water content of about 20 to about 55 weight percent. The polymeric material is comprised of a co-polymer of (a) a hydrophilic monomer, (b) a hydrophobic (aromatic, aliphatic or mixture) monomer, (c) a tris(siloxy)silyl group-containing monomer, (d) a fluorinated monomer containing about 3 to about 20 fluorine atoms per monomer molecule (a polyfluorinated monomer) and (e) an amount of cross-linker sufficient to provide a stress at break value of about 0.003 to about 30N/mm2, elongation at break of about 25 to about 3000 percent and a modulus value of about 0.001 to about 10 N/mm2.
Another polymeric contact lens material comprises a co-polymer of polymerized (a) non-ionic hydrophilic monomer, (b) hydrophobic (aromatic, aliphatic or mixture) monomer, (c) tris(siloxy)silyl group-containing monomer, (d) fluorinated monomer containing about 3 to about 20 fluorine atoms per monomer molecule (polyfluorinated monomer) and (e) cross-linking agent. The weight ratio of the tris(siloxy)silyl group-containing monomer to the non-ionic hydrophilic monomer is about 0.3:1 to about 2:1. The lens material exhibits an oxygen permeability of greater than about 60 Dk units and a water content at equilibrium hydration of about 20 to about 55, and preferably about 35 to about 55 weight percent.
A further embodiment contemplates a polymeric contact lens comprising a co-polymerized (a) non-ionic hydrophilic monomer containing a methacrylamide, an acrylamide, a methacrylate or an acrylate group, (b) a hydrophobic (aromatic, aliphatic or mixture) monomer, (c) a tris(siloxy)silyl group-containing monomer, (d) a fluorinated monomer containing about 3 to about 20 fluorine atoms per monomer molecule (polyfluorinated monomer) and (e) cross-linking agent. The weight ratio of the tris(siloxy)silyl group-containing monomer to the non-ionic hydrophilic monomer is about 0.3:1 to about 2:1. This lens exhibits an oxygen transmissibility of about 60 to about 150 Dk units and a water content at equilibrium hydration of about 20 to about 55, and preferably about 35 to about 55 weight percent.
Yet another polymeric contact lens comprises co-polymerized (a) non-ionic hydrophilic monomer containing a methacrylamide, an acrylamide, a methacrylate ester or an acrylate ester group, (b) fluorinated monomer containing about 3 to about 20 fluorine atoms per monomer molecule (polyfluorinated monomer), (c) tris(siloxy)silyl group-containing monomer, (d) styrene-containing monomer and (e) cross-linking agent. Here, the weight ratio of the tris(siloxy)silyl group-containing monomer to the non-ionic hydrophilic monomer is about 0.3:1 to about 2:1. The lens exhibits an oxygen transmissibility of about 45 to about 150 Dk units and a water content at equilibrium hydration of about 20 to about 55, and preferably about 35 to about 55 weight percent.
A still further polymeric contact lens comprises co-polymerized (a) non-ionic hydrophilic monomer containing a methacrylamide, an acrylamide, a methacrylate ester or an acrylate ester group, (b) fluorinated monomer containing about 3 to about 20 fluorine atoms per monomer molecule (polyfluorinated monomer), (c) tris(siloxy)silyl group-containing monomer, (d) a C1-C10 hydrophobic methacrylate or acrylate monomer and (e) cross-linking agent. Here, the weight ratio of the tris(siloxy)silyl group-containing monomer to the non-ionic hydrophilic monomer is about 0.3:1 to about 2:1. The lens exhibits an oxygen transmissibility of about 50 to about 150 Dk units and a water content at equilibrium hydration of about 20 to about 55, and preferably about 35 to about 55 weight percent.
A further contact lens is the co-polymerization product of a monomer mixture comprising (a) a non-ionic hydrophilic monomer, (b) a tris(siloxy)silyl group-containing monomer, (c) a hydrophobic aromatic monomer such as a styrene-containing monomer, (d) a polyfluorinated monomer, a cationic monomer, a hydrophobic non-aromatic monomer or a mixture of two or three of those monomer types and (e) a cross-linking agent. The monomer mixture includes a weight ratio of tris(siloxy)silyl group-containing monomer to hydrophilic monomer of about 0.3:1 to about 2:1, and a weight ratio of tris(siloxy)silyl group-containing monomer to a single monomer or monomer mixture of (d) of about 1.5:1 to about 20:1. This lens also exhibits an oxygen transmissibility of about 45 to about 150 Dk units and a water content at equilibrium hydration of about 35 to about 55 weight percent.
A still further contact lens is the co-polymerization product of a monomer mixture comprising (a) a non-ionic hydrophilic monomer, (b) a cationic monomer, (c) a tris(siloxy)silyl group-containing monomer, (d) a hydrophobic aromatic monomer such as a styrene-containing monomer, and (e) a cross-linking agent. The monomer mixture includes a weight ratio of tris(siloxy)silyl group-containing monomer to hydrophilic monomer of about 0.3:1 to about 2:1. This lens also exhibits an oxygen transmissibility of greater than 45 Dk units and a water content at equilibrium hydration of about 35 to about 55 weight percent.
A co-polymerization product of a monomer mixture comprising (a) a non-ionic hydrophilic monomer, (b) a poly(dimethylsiloxy)silyl group-containing monomer, (c) a tris(siloxy)silyl group-containing monomer, (d) a hydrophobic monomer, and (e) a cross-linking agent comprises yet another contemplated contact lens. The monomer mixture includes a weight ratio of tris(siloxy)silyl group-containing monomer to hydrophilic monomer of about 0.3:1 to about 2:1, and exhibits a water content on equilibrium hydration of at least 20 weight percent to about 55 weight percent and an oxygen permeation value of about 55 to about 120 Dk units.
A contact lens that comprises a co-polymer of (a) a non-ionic hydrophilic monomer, (b) a tris(siloxy)silyl group-containing monomer, (c) a cationic monomer, (d) a polyfluorinated monomer, a poly-(dimethylsiloxy)silyl monomer, a hydrophobic monomer (aromatic or non-aromatic monomer) or a mixture of two or three of those monomer types and (e) a cross-linking agent is also contemplated. This lens exhibits an oxygen transmissibility of about 45 to about 150 Dk units, and a water content at equilibrium hydration of about 20 to about 55, and preferably about 35 to about 55 weight percent. The lens separately binds mucin and lysozyme in vitro at a ratio by weight of about 1:2 to about 2:1 and in an amount of about 0.75 to about 2.5 xcexcg/cm2, when those proteins are separately present at initial concentrations of 0.46 g/L in aqueous buffers at a pH value of 7.2-7.6.
A polymerization process (or method) is also contemplated. In this process, an ophthalmic contact lens is prepared by the co-polymerization of a monomer mixture that is thermally polymerized in a filled and closed casting cup for time period of about ten to about fifteen minutes at a temperature of about 110 to about 140xc2x0 C., and more preferably at about 120 to about 135xc2x0 C. A contemplated monomer mixture comprises (a) a hydrophilic unsubstituted, mono- or di-substituted C1-C4-alkyl acrylamide or methacrylamide monomer, (b) a tris(siloxy)silyl group-containing monomer, (c) a polyfluorinated monomer, a cationic monomer, a hydrophobic non-aromatic monomer, hydrophobic aromatic monomer or a poly(dimethylsiloxy)silyl group-containing monomer or a mixture of two, three, four or five of those monomer types and (d) a cross-linking agent, in weight ratios discussed elsewhere herein. On completion of the polymerization, the casting cups are cooled, opened, the lenses are removed and the lenses are hydrated for use. A lens so prepared exhibits an oxygen permeability of about 45 to about 120 Dk units and a hydrated water content of about 20 to about 55 weight percent upon hydration.
A further process contemplates an improvement in forming ophthalmic lenses by co-polymerization of a monomer mixture that comprises (a) a non-ionic hydrophilic monomer that is a methacrylamide or acrylamide and (b) a tris(siloxy)silyl group-containing monomer. The improvement comprises wet casting the lenses from a composition that includes those monomers and a non-co-polymerizable solvent that is miscible in the monomer mixture and is readily removable from the co-polymerized lens. In particularly preferred practice, the monomer mixture also includes (c) a poly-(dimethylsiloxy)silyl monomer.
The present invention has several benefits and advantages.
An advantage of the invention is the provision of an ophthalmic lens that provides oxygen sufficient to permit wear of the lens without inflammation or infection for prolonged periods of time.
One benefit of the invention is the provision of an ophthalmic lens that provides water content sufficient to permit wear of the lens without inflammation or infection for prolonged periods of time.
Still further benefits and advantages of the invention will be apparent to a worker of ordinary skill from the discussion that follows.